The four main types of epidermolysis bullosa (EB): dystrophic epidermolysis bullosa (DEB), epidermolysis bullosa simplex (EBS), junctional epidermolysis bullosa (JEB) and Kindler syndrome (KS) are each diagnosed by determining the ultra-structural level at which blisters develop in response to minor traction to the skin.
The subtypes of EB may then be diagnosed on their basis of clinical phenotype, transmission, electron and immunohistochemical findings. An international consensus report on the diagnosis and classification of EB has published phenotypic feature summaries of the EB subtypes.
A specialist dermatologist may be able to make a clinical diagnosis in cases where an informative family tree is available. This is primarily done based on the presenting clinical signs of the patient and personal and family history. The diagnostic tests that are available in some countries include skin biopsies of the blisters that are investigated with procedures such as immunofluorescence mapping (IFM). Transmission electron microscopy (TEM) may also be used in addition to IFM. Genetic testing or mutational analysis, while not routinely done, may also be used.
Patients with severe EB, especially those with recessively inherited EB, need to be evaluated for anemia by using complete blood count and iron studies. Bacterial cultures should be taken from wounds that seem infected or heal poorly. Endoscopy may be used to evaluate for changes in the gastrointestinal tract associated with JEB and DEB. Additionally, the nutritional status of the patient must be evaluated using analyses such as diet diaries, height and weight curves, and serum albumin levels. Examining the range of motion of the extremities and the digits may help assess contractures.
Initial diagnosis of EB mostly happens at birth. The neonatal team then refers the baby to a specialist EB team. In older children, doctors study the child’s skin and investigate the cause of blisters and skin damage as well as the family’s EB history.
When TEM is used, a skin biopsy from a fresh blister is preferred. The biopsy is usually taken from the edge of the blister in order to sample both affected and unaffected skin. The sample obtained is placed in an appropriate holding medium, which typically contains glutaraldehyde and is sent immediately to conduct TEM. Electron microscopy (EM) is the standard means of determining the level of blistering involved in EB. Moreover, EM can provide additional useful information such as blister morphology that aids in making the appropriate EB diagnosis. EBS characteristically has intermediate filament clumping, while JEB has rudimentary hemidesmosomes, and altered or absent anchoring fibrils are usually found in DEB.
IFM can provide even more information on the level of blistering. The biopsy is obtained in the same manner as the one done for TEM. However, a specific medium called Zeus-holding medium is used to temporarily store the sample before analysis. IFM uses antibodies to hemidesmosomal antigen and an antibody to lamina densa protein that assists in distinguishing the different subtypes of EB. In addition to determining the level of blistering, IFM can be used to detect the underlying molecular defects associated with EB. For example, the absence of staining with a specific particular antibody indicates a specific molecular defect.
EB can also be diagnosed prenatally when mutations have been identified in a family. The procedure for obtaining a prenatal sample involves using chorionic villi and these samples may be acquired as early as the 9th week of pregnancy. As an alternative to chorionic villi samples, amniotic fluid may be used after the 11th week of gestation. The obtained fetal samples undergo genetic mutational analysis.
Reviewed by Susha Cheriyedath, MSc